DACULA - More than 200 students and staff members at Dacula High School must be tested for tuberculosis.

The Gwinnett County Health Department has identified 224 students and faculty who were in closest and continuous contact with a 12th-grade student who has a suspected case of the bacterial disease, officials said.

Dacula High Principal Donnie Nutt mailed letters Wednesday to the parents and guardians of students who must be tested. He also sent a letter home Wednesday with every student.

"Although only about 10 percent of our students have been identified as needing testing, I did want to make sure all of our community was aware of the steps being taken as a precaution," Nutt wrote. "Even if your child is not determined to need testing for exposure, you may wish to get an independent opinion from your personal physician."

The Health Department will perform the tests for free Wednesday at Dacula High. A small amount of tuberculin purified protein derivative will be injected just under the skin, which will show if anyone has been exposed to the bacteria that causes tuberculosis. Health officials will return to the school two days later to evaluate the results, said Vernon Goins, a health department spokesman.

Parents must sign permission slips for students to receive the free testing. Students who are not tested at the school can have a test performed by a private physician, but the results must be reported the Health Department.

Tuberculosis "is a very slow growing bacteria, and it's probably one of the slowest to grow," Goins said. "That means it's easy to control, but it can be difficult to detect."

The Health Department was notified Feb. 5 of the student's possible infection, Goins said. The case is not active, and it's possible the student does not have the disease, he said.

Exposure to tuberculosis does not guarantee an infection, but anyone who is infected can be treated for six to nine months with antibiotic therapy and anti-tuberculosis drugs.

Eight to 10 weeks after health officials perform the initial tests, the department will return to the school retest everyone who did not show signs of a tuberculosis infection, Goins said.

Anyone who shows signs of a possible infection must make arrangements to have a chest X-ray. If the X-ray shows signs of tuberculosis, the next step is a sputum test, in which people cough deeply to expel material from their lungs.

If anyone tests positive for tuberculosis, he or she must have three clear sputum tests before returning to school, Goins said.